Vapor Pressure, Decomposition , and Temperature

[InDepth]

Does anyone know of any liquid that when heated increses its vapor pressure, but while being heated decomposes to another chemical, and then starts reducing its vapor pressure?

i.e. Vapor pressure would increase and suddenly or gradually decrease with temperature due to heat decomposition?

 

[dcasto]

heat of decompositions is exothermic, how could you get lower pressure as the temperature rises? And at decomposition, you get more molecules subject to pv=nRt

 

[ash9144]

Sort of, you could have a monomer that as it heats the vp goes up until it reaches the point it polymerizes then it would turn into a polymer with much less vp. Such as VCM.

 

[dcasto]

polymerize is not decomposition.

 

[InDepth]

ash9144 and dcasto, I'm not a chemical engineer, so bear with me. Maybe decomposition is not the right term, but I am looking for something that behaves like what ash9144 indicated. Is there a monomer that polymerizes and reduces its vp? I'm looking for this special case.

 

[Compositepro]

Styrene, ethylene, propylene, vinyl chloride, formaldehyde, and numerous others have significant vapor pressure and will polymerize. Polymerization is exothermic so temperature control can be a problem.

 

[ash9144]

Decomposition reaction is generic term for reaction leading to more molecules. It will be exo or endo thermic depending on physical properties.

Polymerization reaction takes many molecules and makes one really big molecule

So something like vinyl chloride monomer or styrene would have increasing vapor pressure with increasing temperature. Then would rapidly polymerize giving off large amounts of heat. Then you would a blob of polymer with a significantly lower vp than the monomer you started with.

 

[InDepth]

For styrene (or ethylene, propylene, vinyl chloride, formaldehyde):
1) What temperature does it polymerize to ploystyrene?
2) What is the vapor pressure of styrene prior to polymerization?
3) What is the vapor pressure of polystyrene just after polymerization?

If someone has a plot or reference, that would be great. Or point me to a place where I can find this info. I'm having a hard time finding information for these materials outside of NTP/STP

 

[25362]

Vapor pressure, in Pa, of styrene, following Perry's Chem. Eng. Handbook, 8th Ed., McGraw-Hill:

ln P = C1 + C2/T + C3.lnT +C4.T^C5​

C1 = 105.93
C2 = -8685.9
C3 = -12.42
C4 = 7.5583 E-06
C5 = 2

between T_min = 242.54 K (melting point) and T_max = 636 K.

P at T_min = 10.6
P at T_max = 3.823 E+06

Perry also gives a table of vapor pressures in mm Hg between 1mm and 760 mm Hg.

Left alone at room temperature, styrene will eventually polymerize with itself to a clear glassy solid. Technical grade styrene is 99% minimum purity. It is shipped with a polymerization inhibitor in it, in standard tank cars or trucks.